It concerned with discovering psychological processes that make it possible for human beings to acquire and use language. We want to remember, in earlier years (at age five) whether there was nobody who taught on syntactic, phonological, morphological and semantic rules of grammar of language. It is obvious that children do not learn a language by memorizing the sentences of language and storing them rather they have acquired a system of rules that enable them to construct and understand sentences they have never heard or produced before. How do children acquire such intricate system so quickly and effortlessly